Enhancing the dispersibility of Gelidium amansii-derived microfibrillated cellulose through centrifugal fractionation

Hydrothermal pretreatment is useful for microfibrillated cellulose (MFC) preparation due to its safety, but the remaining hemicellulose might affect MFC properties. This study aimed to investigate the effect of centrifugation time on hemicellulose removal and the physicochemical properties of MFC obtained after hydrothermal pretreatment and micro-fibrillation. In this study, centrifugation was applied to the MFC suspension at varying duration times. Composition analysis and Fourier transform infrared spectra indicated that fractionated MFC has no hemicellulose content after 10, 20, and 30 min centrifugation. It also showed an approximately 5 times higher than 0.5 % g/g of initial solid concentration, indicated by a lower gel concentration point, than unfractionated MFC. Scanning electron microscope images of the fractionated MFC for 30 min (MFC2C) presented thin, long cellulose fibrils of 517 nm in average diameter and 635-10,000 nm in length that induced a slower sedimentation rate. MFC2C dispersion was also improved by autoclave sterilization by regulating cellulose structure, rheology, and crystallinity. As a result, MFC dispersibility can be enhanced by removing hemicellulose through simple centrifugation.

Macroalgae culture-induced carbon sink in a large cultivation area of China

Macroalgae culture-induced carbon sink in sediments has been little investigated. Here, total organic carbon (TOC), total nitrogen (TN), and δ13C were examined in sediments in a cultivation field of macroalgae (kelp and Gracilariopsis lemaneiformis) in Sansha Bay, Southeast China. Both proxies of C/N (TOC to TN ratio) and δ13C indicated a multisource of TOC. Based on a three-endmember model, macroalgae-derived TOC (TOCma) accounted for < 35% of the total TOC, averaging 16 ± 9% (mean ± SD). On average, terrestrial and phytoplankton-derived TOC showed much higher percentages of 24 ± 17% and 60 ± 20%, respectively (t-test, p < 0.02). A preliminary estimate suggested that TOCma represents a carbon sink of 8.2 × 103 tons per year, corresponding to about 22% of the sink associated with phytoplankton and macroalgae and 8 ± 6% of the macroalgae carbon production in Sansha Bay. Considering its production magnitude, the macroalgae-induced carbon sink seems to be insignificant, on a national or global scale, to phytoplankton, though it should be taken into account given the small cultivation area.

Composition of deposited sediment and its temporal variation in a disturbed tropical catchment in the Kelantan river basin, Peninsular Malaysia

Pristine tropical river systems are coming under increasing pressure from the development of economic resources such as forestry and mining for valuable elements. The Lebir catchment, north eastern Malaysia, is now under development as a result of unregulated tree felling and mining for essential and rare metals. Two sediment cores, one in the upstream reaches and the other from the downstream reaches, were taken from flood prone area of the Lebir River, Malaysia, and analysed for their elemental composition by XRF, specifically Al, Si, Fe, Ca, K, Mg, Mn, V, Cu, Ni, Pb, Cr, Zn, As, Th and U. Activities of fallout radionuclides, ¹³⁷Cs and ²¹⁰Pb were also determined to from a geochronological context. The elemental concentrations in the soils were assessed in terms of their enrichment factor and Si, Ca, K, Mg, Mn, V, Cu, Ni and Zn were found not to be enriched, whereas As, Th and U had elevated enrichment factors. The Th and U were particularly enriched in the downstream core indicating inputs from a tributary that drains a catchment with known deposits of Th and possibly U. The results suggest that the growth in economic development is fostering the transport of contaminants by the major rivers which, in turn, is contaminating the riverine floodplains. This points to the need for a more integrated and holistic approach to river basin management to maintain the environmental quality of these fragile aquatic systems.

Suspended sediments mediate microplastic sedimentation in unidirectional flows

Microplastic particles (MP) are an emerging contaminant threatening many aquatic systems. Because of the sharp increase in plastic manufacture, the concentration of MP in natural ecosystems has grown dramatically. While it is known that when MP enter aquatic ecosystems they are transported and dispersed via different mechanisms (currents, waves, turbulence), the processes involved are still poorly understood. In the current study, the transport of MP by a unidirectional flow has been investigated in a laboratory flume. MP enter the system through a plume that can (or not) have suspended sediment. The interaction between MP and sediment was studied for three different MP particle types (Polyamide (PA) and Polyvinyl Chloride (PVC) fragments, and Polyethylene Terephthalate (PET) fibers), and four different sediment concentrations (0 g/l, 15 g/l, 30 g/l and 45 g/l). In all cases, sediment increased the vertical transport of MP to the bottom. The greater the sediment concentration, the greater the downward flux of MP. Sediment particles scavenged PA fragments downwards at the highest rate, followed by PET fibers and finally PVC fragments. These results indicate that a sediment particle-laden plume carrying MP may induce a differential settling of MP as they are advected. The scavenging of MP by sediments may result in sedimentation segregated patterns, with MP being found at shorter distances than expected for the case without sediment, therefore increasing the presence of MP near their contaminant sources.

Efficiency evaluation of titanium oxide nanocomposite membrane in adsorption of chromium from oil effluents

Reverse osmosis and nanofiltration (NF) are the essential physical separation technologies used to remove contaminants from liquid streams. A hybrid of nanofiltration and forward osmosis (FO) was used to increase the removal efficiency of heavy metals in synthesized oil effluents. Thin-film nanocomposite (TFN) membranes were synthesized by applying surface polymerization on a polysulfone substrate to use in the forward osmosis process. The impact of different membrane fabrication conditions such as time, temperature, and pressure on effluent flux, the effect of different concentrations of the heavy metal solution on adsorption rate and sedimentation rate, the impact of TiO₂ nanoparticles on the performance and structure of forward osmosis membranes were investigated. The morphology, composition, and properties of TiO₂ nanocomposites made by the infrared spectrometer and X-ray diffraction (XRD) were studied. Kinetic modeling and Langmuir, Freundlich, and Tamkin relationships were used to draw adsorption isotherms and evaluate adsorption equilibrium data. The results indicated that pressure and temperature directly affect water outlet flux, and time affects it indirectly. Evaluating the isothermal relationships revealed that chromium adsorption from the TFN 0.05 ppm membrane and thin-film composite (TFC) membrane follows the Langmuir model with correlation coefficients of 0.996 and 0.995, respectively. The significant removal of heavy metals and the acceptable amount of water flux demonstrated the appropriate potential of the titanium oxide nanocomposite membrane, which can be used as an effective adsorbent to remove chromium from aqueous solutions.

Chronostratigraphy elucidates environmental changes in lacustrine sedimentation rates and metal accumulation

All changes taking place in a watershed have repercussions on lacustrine environments, being these, the sink of all activities occurring in the basin. Lake Titicaca, the world's highest and navigable lake, is not unfamiliar with these phenomena that can alter the sedimentation dynamics and metal accumulation. This study aimed to identify temporal trends of sedimentation rates by employing a geochronological analysis (²¹⁰Pb, ¹³⁷Cs) and to propose metal background values in Puno Bay, as well as to identify metal concentrations (As, Ba, Ca, Cr, Cu, K, Mg, Mo, Ni, Pb, Zn) in the projected timeline to propose, for the first time, background values in Puno Bay. Two sediment cores were collected from the outer and inner bays. Sediment rate (SR) was calculated through the excess of ²¹⁰Pb (²¹⁰Pb_xs) applying the Constant Flux Constant Sedimentation (CFCS) model. Results show that SR in the outer bay was 0.48 ± 0.08 cm a^-1 and for the inner bay was 0.64 ± 0.07 cm a^-1. Sediment quality guidelines (SQGs) did not indicate toxicity was likely to occur, except for As. However, enrichment factors (EFs) indicated that all metal accumulation is geogenic. Climatic factors had a marked influence on sedimentation rates for the outer bay, and in the case of the inner bay, it was a sum of climatic and human-based factors.

Changes in the carbon source and storage in a cultivation area of macro-algae in Southeast China

Macro-algae culture has recently attracted attention in China because of its capability to sequester carbon. Here, radionuclides, total organic carbon (TOC), and nitrogen (TN) were examined in a cultivation area of macro-algae in Southeast China. At the reference site, the ratio of TOC to TN (C/N, 8.1 ± 0.2, mean ± SD) did not exhibit discernible variation over the past 70 years. In contrast, in the cultivation area, C/N descended from 9.0 ± 0.2 around 1960 to 8.3 ± 0.2 between 1960 and 1990 and 7.6 ± 0.2 after 1990, coincident with the recorded kelp production in this area, indicating an influence of macro-algae culture-associated activities on carbon origin. Using a model, algal culture-associated activities contributed 23 ± 7 % between 1963 and 1990 and 53 ± 8 % between 1990 and 2022 to TOC. The burial of culture-associated TOC varied from 0.15 to 1.23 mg-C cm^-2 yr^-1, implying the unneglectable influence on carbon storage.

Sediment organic carbon dynamics response to land use change in diverse watershed anthropogenic activities

Sediment organic carbon (SOC) is a precious archive that synthesizes anthropogenic processes that remove geochemical fluxes from watersheds. However, the scarcity of inspection about the dynamic mechanisms of anthropogenic activities on SOC limits understanding into how key human factors drive carbon dynamics. Here, four typical basins with similar natural but significantly diverse human contexts (high-moderate-low disturbance: XJ-ZS and YJ-LS) were selected to reconstruct sedimentation rates (SR) and SOC dynamics nearly a century based on 200-cm corers. A partial least squares path model (PLS-PM) was used to establish successive (70 years) and multiple anthropogenic data (population, agriculture, land use, etc.) quantification methods for SOC. Intensified anthropogenic disturbances shifted all SR from pre-stable to post-1960s fluctuating increases (total coefficient: high: 0.63 < low: 0.47 < medium: 0.45). Although land use change was co-critical driver of SOC variations, their trend and extent differed under the dams and other disturbances (SOC mutated in high-moderate but stable in low). For high basin, land use changes increased (0.12) but dams reduced (-0.10) the downstream SOC. Furthermore, SOC mutation corresponded to soil erosion due to urbanization in both periods A and B. For moderate, SOC was reversed with the increase in afforestation and cropland (-0.19) due to the forest excitation effect and deep ploughing, which corresponded to the drought in phase B and the anthropogenic ecological project in A. For low, the increase in SOC corresponded to the Great Leap Forward deforestation in period B and the reed sweep in A, which suggested the minor land change substantially affected (0.16) SOC in fragile environments. Overall, SOC dynamics revealed that anthropogenic activities affected terrestrial and aquatic ecosystems for near the centenary, especially land use. This is constructive for agroforestry management and reservoir construction, consistent with expectations like upstream carbon sequestration and downstream carbon stabilization.

Chronology of trace elements and radionuclides using sediment cores in Golden Horn Estuary, Sea of Marmara

Trace elements and radionuclides are substantial pollutants in marine environment since they are non-biodegradable and can be harmful even in minute concentrations. The Golden Horn estuary, where is an inlet of Bosphorus and two creeks, has been seriously polluted by untreated municipal and industrial dischargers for several decades. Since 1998, a large restoration and rehabilitation efforts have been undertaken in the estuary to mitigate the pollution. In the present study, four sediment cores were taken from the Golden Horn estuary to assess the historical accumulation of trace elements and radionuclides. Radiometric dating was implemented by ²¹⁰Pb and ¹³⁷Cs radionuclides and CRS model. Sedimentation rates were calculated in the range of 0.92-0.97 cm yr^-1 in the estuary. The distribution of radionuclides (⁴⁰K, ²²⁶Ra, and ²²⁸Ra) indicated some slight variations which ascribes to the geological characteristics of sediment along the cores. The concentrations of the anthropogenic elements were relatively higher in the intensive industrialization period. Their concentrations reduced in the latest 15-20 years thanks to the large-scale rehabilitation project in the estuary. The pollution indices, namely EF, Igeo, CF, and PLI showed that the concentrations of Cd, Cr, Cu, Pb, Sb, and Sn were above the world averages. Our results provide an insight on the long-term accumulation trends of trace element in the Golden Horn, which revealed that the estuary remains moderately polluted. We suggest that preventive countermeasures are much more important than post pollution remediation in the case of metallic pollution in the estuaries.

Assessment of the distribution and ecological risks of heavy metals in coastal sediments in Vietnam's Mong Cai area

Coastal sediments in the Mong Cai area were collected and analyzed for grain size, heavy metals, total organic carbon, and isotopes (²¹⁰Pb, ²²⁶Ra, δ¹⁵N, δ¹³C) to assess sediment quality. The most common sediments were fine sand in surface sediment, very fine sand in core C1, and very coarse and coarse silt in core C2. The total organic carbon was highest in C2 next to the surface and lowest in C1, with content levels of 1.81%, 0.40%, and 0.31%, respectively. The chronology in C1 was 1877-2019 (142 years, 0-5 0 cm), with an average sedimentation rate of 0.71 cm/year. In C2, the chronology was 1944-2019 (75 years, 0-14 cm), with an average sedimentation rate of 0.27 cm/year. These δ¹³C and δ¹⁵N in the sediment reflect the source of the organic matter mix from the marine and terrigenous sediments. All studied heavy metals were lower than the ISQGs, with the exception of As in C1 and C2, which were higher. C1 showed a decline in As over time, while C2 As levels increased between 1996 and 2019. In terms of heavy metal pollution indexes, the geoaccumulation index (Igeo) showed that C1 and C2 were unpolluted to moderately polluted with As, with Li and Pb in C2; the enrichment factor (EF) was moderately enriched with As; the contamination factor (CF) was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and C1 (Cd, As, Li) and considerably contaminated (As) in C2. The risk factor (ER) of As showed a moderate potential ecological risk in C2. The degree of contamination (CD) ranged from moderate to considerable (C1, C2), and the ecological risk (RI) was low. Although CD ranged from moderate (C1) to considerable (C2), most contamination was concentrated at the bottom of the cores. RI was low. The Mong Cai sediment quality does not currently affect the coastal area's ecosystem and fauna.

Response of sedimentation rate to environmental evolution in Da River Reservoir in Southwest China

Lake sediment records the evolution process of the interaction between human and nature. It is important to master the lacustrine sedimentation rate for the ecological environment assessment of catchment. A 60-cm sediment core was collected in the Da River Reservoir during 2019 to analyze radionuclides (²¹⁰Pb and ¹³⁷Cs) massic activities, grain size, total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), and metals (Mn, Cu, Al, and Pb) mass fractions to reconstruct the response of sedimentation rate to environmental evolution. The environmental changes in the small catchment were classified into the following three stages through cluster analysis (CA) for geochemical parameters in the sediment core: phase I (1881-1985), phase II (1987-1999), and phase III (2000-2018). The average depth sedimentation rates (ADSRs) of the three stages were 0.33, 0.90, and 1.50 cm/year, respectively. The sedimentation rates increased from the bottom to the surface layer, indicating that the exogenous inputs into the reservoir have been occurring. The sediment deposition in phase III was strongly disturbed by the environmental changes (such as warmer climate and intensified land use). Therefore, sedimentation rates showed a rapid increase. Both Pearson correlation analysis and redundancy analysis (RDA) showed that sedimentation rates were positively correlated with climatic factors, particle size, nutrients and metals mass fractions, elemental ratios, and socioeconomic parameters. Sedimentation rates show high sensitivity to anthropogenic activities and climatic change, which can be used to reconstruct the environmental evolution process at a small catchment scale.

Microalgal flocculation and sedimentation: spatiotemporal evaluation of the effects of the pH and calcium concentration

The high cost of harvesting microalgae is a major hurdle for the microalgae industry, and an efficient pre-concentration method is required. In this study, the effects of using different pH values (between pH 3 and 11) and calcium (Ca²⁺) concentrations (between 0 and 5 mM) on Chlorella vulgaris sedimentation were investigated by evaluating the spacio-temporal distributions of microalgae cells. Fast and efficient sedimentation occurred (within 10 min) at a high Ca²⁺ concentration (5 mM) at pH 9 and 11. However, the sediment volume was lower at a Ca²⁺ concentration of 3 mM than at a Ca²⁺ concentration of 5 mM. This indicated that the Ca²⁺ concentration strongly affected the sediment volume. Fast sedimentation and a low sediment volume were found at pH 7 and a Ca²⁺ concentration of 5 mM, probably because of the neutral charge in the system (adhesion to calcium precipitates would have occurred at a high pH). The highest Ca²⁺ recovery (82%) was achieved when sediment produced at pH 11 and a Ca²⁺ concentration of 5 mM was acidified to pH 3.

The dataset for the chronology of the sedimentation in the Danube abyssal fan which records the major episodes of the late-Holocene Black Sea evolution

Anoxic marine sediments at the confluence with large rivers are key archives for monitoring the anthropogenic impact in the environment and asses the carbon sink character of oxygen deprived waters. This data article describes the analysis methodology and the results of the deep-sea sediments sampled from the NW part of the Black Sea, using the ¹⁴C dating, stable carbon isotopes, C/N ratio, metallic traces and ²¹⁰Pb and ¹³⁷Cs radioactivity. For this purpose, 26 sediment samples were taken from the MN183-3 sampling point (43.925.917 N, 30.758.911 E, 658 m water depth) using a Mark II-400-type multicorer. The samples were collected during the two weeks Mare Nigrum (MN) #183 marine expedition, which took place at the beginning of September 2018, in the Romanian section of the Black Sea shelf and continental slope. These analyses were employed in the construction of a Bayesian high-resolution sedimentation model, reported in M.Ilie et al. (2022).

Ecological risk assessment of the riverine and deltaic environments (Rozechai River, Urmia Lake, Iran), using sediment quality indices

Rozechai River is one of the tributaries of Urmia Lake (the nrthwest of Iran), which has experienced severe pollution and water level fluctuations in the coastal zone over the past four decades. The present study aimed to assess the ecological risk for aquatic life and human health. Research methods were designed for applying the sediment quality guidelines (LEL, PEL, SEL), sediment quality indices (C_f, C_d, E_r, RI), and enrichment factor (EF) based on the concentration of toxic metals in sediments. Event-based geochronology of the sediment column showed that the high stands in the water level of the Urmia Lake (> 1274 m) occurred in 1983, 1989, and 1995. Thus, As, Pb, Zn, Cd, Cr, and Ni reached a moderate to considerable enrichment under the oxidation and alkaline condition. Consequently, a moderated level of ecological risk index (RI) was predominant between 1983 and 1999. The uppermost 35 cm of the sediment column was deposited during a severe drought period to which H₂S bearing water and reducing status contributed. In such conditions, the low ecological risk was resulted in the basin due to the lower rate of the toxic metal influx. The industrial, urban, and agricultural wastewaters contributed to the release of toxic metals and the dominance of moderate to considerable enrichment, which led to a moderate ecological risk at the coastal zone of the Rozechai River. The sediment column of the deltaic area has experienced a mean sedimentation rate of 1.66 cm year^-1 since 1982.

Geochemistry and sedimentary photopigments as proxies to reconstruct past environmental changes in a subtropical reservoir

Sediment cores were used to establish past environmental impacts associated with eutrophication, erosion and metal contamination in the subtropical Atibainha reservoir (São Paulo State, Brazil). We hypothesize that: (1) the levels of nutrients, determined by a spectrophotometric method, reflect the contributions of these elements over time and (2) changes in sedimentation rates, determined by ²¹⁰Pb geochronology, and metal flows, determined by ICP-AEOS, are related to anthropic activities. Stratigraphic changes in the analysed variables were used to divide the sediment cores into three intervals, according to PCA and cluster analysis (Euclidian distances, Ward's method). Interval I, composed by the period prior to operation of the reservoir, was influenced by organic matter levels. Interval II, between 1967 and 1993 (PC2: 14.94% of the total variability), a period of minor impacts, was mainly influenced by Mn (eigenvalue of 0.71) and Zn (0.74). Interval III, which included sediment deposited between 1993 and 2015 (PC1: 60.28% of the total variability), was influenced by the highest levels of the pigments lutein (0.86), zeaxanthin (0.90) and fucoxanthin (0.65), together with total nitrogen (0.78) and sedimentation rate (0.91), suggesting changes in the phytoplankton community composition probably associated to the intensification of eutrophication and erosion processes. Despite the limitations of applying paleolimnological techniques in reservoirs and the use of pigments as proxies in regions with higher temperatures, it was observed that the anoxic conditions and the aphotic environment in the hypolimnion acted to preserve pigments associated with the groups Chlorophyta (lutein), Cyanobacteria (zeaxanthin) and Bacillariophyta (fucoxanthin). The isolated analysis of nutrients was not sufficient to make conclusive inferences regarding the eutrophication history, since the levels of TP tended to decrease over time, in contrast to an increase in the levels of TN. Despite intensification of eutrophication and erosion, associated to anthropic activities, no signs of metal contamination were recorded.

Sedimentation rates and sediment age of the high-altitude cold desert Ramsar Wetland, the Chandratal, inferred from radionuclide (210Pb and 137Cs) technique

In the current scenario, the pristine Himalayan Wetlands are under endangerment due to higher sedimentation rate, including siltation, reduction of ecological value, pollution, and significant anthropogenic encroachment along with advanced civilization. The more increased sedimentation reduces the depth and existing expansion of the Wetland. This study articulates the record of sedimentation in the Chandratal present in Western Himalaya, Himachal Pradesh, India, at the altitude of 4300 m. The sedimentation rate of the Chandratal was calculated based on a 1-m core sample considering isotopes of ¹³⁷Cs and ²¹⁰Pb dating techniques. The present study based on the Constant Rate of Supply (CRS) model of ²¹⁰Pb reveals that the Wetland experienced an average sedimentation rate of 1.75 ± 0.04 cm/year during the last 63 years observed from 1953 to 2016. The ¹³⁷Cs peak method-based calculated sedimentation rate of the Chandratal is 1.6 ± 0.02 cm/year representing the years for about 62 years from 1954 to 2016. The Wetland's functional survival prevalence was estimated to be 420 and 459 years based on ²¹⁰Pb and ¹³⁷Cs dating techniques, respectively. The study communicates that the magnified human interference in the catchment area of the Chandratal is accountable for the faster sedimentation in recent years.

Heavy metals and Pb isotopes in a marine sediment core record environmental changes and anthropogenic activities in the Pearl River Delta over a century

Heavy metal accumulation in marine sediments is associated with changes in both the natural environment and human activities. This study used heavy metals and Pb isotopes in a precisely dated (by ²¹⁰Pb and ¹³⁷Cs) sediment core from the Macao Sea to reconstruct the historical changes in anthropogenic activities and the environment in the western Pearl River Estuary (PRE). The distribution of heavy metals in the sediment core could be divided into four stages (pre-1950, 1950-1976, 1976-2000, and post-2000), which corresponded to the changes in anthropogenic activities and environment of the Pearl River Delta during the past 100 years. The contribution of anthropogenic metals (Pb and Zn) in the sediments increased gradually over time. However, the concentrations, enrichment factors, and fluxes of heavy metals in the sediments all displayed a downward trend since 2010, revealing a decline in metal pollutant input due to strict emission reduction policies implemented in the last decade. The Pb isotopes in the sediments showed a similar trajectory to the heavy metals, reflecting the changes in Pb sources in the sediments at different stages. Based on a binary Pb isotope mixing model, the calculated proportions of anthropogenic and natural Pb in the sediments were 0-50.9% (mean 15.9%) and 49.1-100% (mean 84.1%), respectively, suggesting that the Pb in the PRE sediments is mainly controlled by natural sources.

Sedimentation rates by the 210Pb chronological method in Itanhaém river watershed, southeast Brazil

The historical variation of sedimentation rate was investigated in five cores collected from the Itanhaém watershed main rivers, the second largest coastal watershed of the São Paulo state, Brazil, using the lead-210 radioisotope as a geochronometer. The main characteristics of the rivers' waters and sediments were determined in order to support the geochronological analysis results and associate sediments with possible source areas. In this context, the fluvial waters' general classification indicated the facies sulfated or chlorinated sodium in the winter and summer seasons, except for the Branco river waters in summer, which were classified as calcium or magnesium bicarbonate. A longitudinal salinity gradient was found in the downstream river courses, under greater marine influence, with the ions Cl^-, Na⁺, SO₄²⁺, Mg²⁺, Ca²⁺, and K⁺ being most common in the waters. Silica is the predominant constituent in the sediment cores and is inversely related to the organic matter (OM) presence. Inverse correlations were also found between silica and other constituents. The watershed sedimentation rates were determined in the range of 0.31 up to 3.97 g/cm²/year and 0.30 up to 3.40 cm/year, highlighting the core extracted from Branco river, which showed the highest sedimentation rate. The profiles corresponding to Preto and Aguapeú rivers presented discontinuities in the sedimentation rates. The discontinuities were dated and would probably be related to the anthropic activities, which intensified in the municipality of Itanhaém around the middle of the twentieth century.

Chernobyl still with us: 137Caesium activity contents in seabed sediments from the Gulf of Bothnia, northern Baltic Sea

Anthropogenic radionuclides are among those human impacts, which can be seen widely in the marine and terrestrial ecosystems. Fallout from the 1986 Chernobyl nuclear power plant accident has rendered the Baltic Sea as the most polluted marine body in the world with respect to ¹³⁷Cs. This research investigated sediment cores from 56 sites around the Gulf of Bothnia, Baltic Sea. Radioactivity from ¹³⁷Cs in sediments has generally declined due to natural/radioactive decay of ¹³⁷Cs over the last decades. However, ¹³⁷Cs contents in subsurface sediments remain at elevated levels compared to pre-Chernobyl levels. The highest ¹³⁷Cs activity contents in subsurface sediments (>4000 Bg kg^-1) occur in coastal areas including estuaries. These areas often experience severe anthropogenic pressure. The southern Bothnian Sea, Kvarken archipelago, and southern Bothnian Bay all show elevated ¹³⁷Cs values in subsurface sediments. Sedimentary ¹³⁷Cs can also help constrain recent rates of sedimentation. Post-Chernobyl sedimentation rates in the Gulf of Bothnia varied from 0.1 to 4.8 cm/year with an average sedimentation rate of 0.54 cm/year.

Production rate variation and changes in sedimentation rate of marine core dated with meteoric 10Be and 14C

The first measurement of meteoric beryllium-10 (¹⁰Be) using Accelerator Mass Spectrometer (AMS) is reported from PRL-AURiS (Physical Research Laboratory-Accelerator Unit for Radioisotope Studies). Strategically, the meteoric ¹⁰Be dating method can date events as old as 10 Myr, and its accuracy while dating marine sediment cores has been well tested with magnetic methods. An attempt is made for a comparative study between radiocarbon (¹⁴C) and meteoric ¹⁰Be dating methods from a 6 m long sediment core collected from the equatorial Indian Ocean. The core was dated using both radiocarbon and meteoric ¹⁰Be and results showed remarkable similarity for both methods in terms of the sedimentation rate. A continuous age offset observed within 50 kyr could be due to a continuous influx of sediment with low ¹⁰Be content and that may have caused the meteoric ¹⁰Be ages to be younger. The sedimentation rate calculated by changing the ¹⁰Be depositional flux rate from 1.5 to 2.5 × 10^-2 atoms.cm^-2.s^-1 shows large variation, indicating the choice of appropriate ¹⁰Be depositional flux rate for the region. Additionally, being the first meteoric beryllium-10 measurements using AURiS, we have also discussed and reported the laboratory protocols and efficiency based on repeat standard and blank measurements.

Reconstruction of sedimentation rates based on the chronological framework of Lake Pykara, Tamil Nadu, India

This work presents a piece of initial information about the estimation of the sedimentation rate for Lake Pykara. In this investigation, a chronological sequence of sediment core was set up dependent on ¹³⁷Cs and ²¹⁰Pb_ex analysis to study sediment accumulation rates in Lake Pykara. Caesium-137 (Cs) is an artificial radionuclide and is regularly utilized in building up the chronology of lake sediments in the Anthropocene period. The unsupported ²¹⁰Pb profile shows a non-exponential decline of ²¹⁰Pb activity with sediment depth. Sedimentation rates dependent on global atmospheric nuclear weapon maximum fallout of ¹³⁷Cs (1963) bolster the utilization of the consistent rate of ²¹⁰Pb supply (CRS) model in core sediments. The geochronology studies of the core were performed using the ¹³⁷Cs method, to evaluate the model of time changes in the sediment. The ¹³⁷Cs radioactivity was resolved directly by gamma spectrometry and fluctuated from 13.11 ± 1.3 Bq kg^-1 for top layers to 1.21 ± 0.1 Bq kg^-1 for the bottom of the core. Two trademark peaks of ¹³⁷Cs radioactivity identified with the global fallouts after atomic weapons testing and the Chernobyl mishap were observed and used to affirm the ²¹⁰Pb dating method. Radioactivity of ²¹⁰Pb_ex ranged from 8.00 ± 1.0 to 1.40 ± 0.1 Bq kg^-1. The mean sedimentation rate evaluated from both models was 0.71 ± 0.06 cm year^-1, while the estimated age of Lake Pykara was 514.08 years (¹³⁷Cs) and 521.43 years (²¹⁰Pb_ex), respectively.

An eco-parametric method to derive sedimentation rates for coastal saltmarshes

The saltmarsh plant Spartina alterniflora was introduced to the Jiangsu coasts, China and serves as an ecological engineer to reduce near-bed shear stress, trap fine-grained sediments and protect the coast from wave-induced erosion. The saltmarshes thus could record the Spartina colonization-driven changes within the sedimentary layers. Based on these ecological and sedimentological changes in sediments, we present a new eco-parametric method to estimate the sedimentation rate for the newly-formed wetlands in the Yancheng Wetland Nature Reserve for Rare Birds, Jiangsu. Sediment cores and satellite imagery were used to identify the thickness of accumulated sediment layers and the time since the Spartina colonization. We defined the original ground on which Spartina alterniflora initially colonized using pigment concentrations, grain size and stable carbon isotopic compositions of organic matter (δ¹³C) in sediments. We also determined the time mark of the Spartina colonization by examining the Landsat images over 1982-2018 to discriminate the Spartina alterniflora from other native plants and geomorphological features. These two datasets yielded a sedimentation rate of 3.3 cm/yr for Core A and of 9.6 cm/yr for Core B, the latter evidenced by an increase of ~ 0.51 m in the bed level from 2008 to 2014. Combining the ²¹⁰Pb dating method, we further estimated the sedimentation rate for the layers beneath the original ground, which was comparable to that of the bare flats in the Jiangsu coast. Even though this new method is only applicable to newly-formed saltmarshes, it helps identify the recent sedimentation events as well as reveal the environmental changes and the evolution of saltmarsh-bare flat systems due to the interplay between vegetation, hydrodynamics and sediment dynamics. It thus could be an efficient and cost-effective tool for an improved understanding of the response of coastal wetlands to a changing climate/environment.

Use of natural and artificial radionuclides to determine the sedimentation rates in two North Caucasus lakes

The specific activities of natural (²¹⁰Pb, ²²⁶Ra, and ²³²Th) and artificial (¹³⁷Cs, ^239,240Pu, and ²⁴¹Am) radionuclides in the sediments of two North Caucasus lakes were determined. The two lakes, Lake Khuko and Lake Donguz-Orun, differ in their sedimentation conditions. Based on the use of unsupported ²¹⁰Pb_ex and both Chernobyl-derived and bomb-derived ¹³⁷Cs as chronological markers, it was established that the sedimentation rates in Lake Khuko over the past 55-60 y did not exceed 0.017 cm y^-1. Sedimentation rates in Lake Donguz-Orun were found to be more than an order of magnitude higher. In the latter case, the sedimentation rates for the period from 1986 to the present were over 1.5 times higher than they were for the period 1963-1986. The differences in sedimentation rates were due to differences in the rates of denudation of their respective catchment areas. The specific activities of artificial radionuclides (¹³⁷Cs, 2600 Bq kg^-1; ^239,240Pu, 162 Bq kg^-1; and ²⁴¹Am, 36 Bq kg^-1) and their ratios in the sediments of Lake Khuko show that their deposition was mainly due to global stratospheric fallout of technogenic radionuclides associated with nuclear bomb testing during 1954-1963-rather than fallout from the Chernobyl accident. Several factors, including the mode of precipitation, features of the surface runoff, and location of Lake Khuko, were responsible for the accumulation of artificial radionuclides.

210Pb dating of recent sediments from the continental shelf of western India: factors influencing sedimentation rates

Several cores from the continental shelf of the Arabian Sea along the Indian Coast were investigated for change in sedimentation rates duly constrained for chronology based on ²¹⁰Pb and ¹³⁷Cs dating techniques. The emphasis was to look for spatial and temporal variation in the sedimentation rate along the continental shelf of eastern Arabian Sea between Goa to Kochi for water depth ≤ 150 m. This study showed varying sedimentation rates in coastal and distant sediment cores. Both ²¹⁰Pb and ¹³⁷Cs dating techniques showed comparable sedimentation rate in most sediment cores. The sedimentation in the continental shelf region of the coastal Arabian Sea is primarily controlled by discharge of sediments from rivers during Indian summer monsoon. Increased sedimentation rate from the north (off Goa) to the south (off Kochi) was triggered by high riverine flux and longshore sediment transport.

Sedimentation rate-based screening of oleaginous microalgae for utilization as a direct combustion fuel

The co-combustion of microalgae biomass with coal has the potential to significantly reduce CO₂ emissions by eliminating expensive and carbon-emitting downstream processes. In this study, the utilization of microalgal biomass as a direct combustion fuel in co-firing industries and the screening of potential oleaginous strains of high calorific value was investigated. High-lipid accumulating mutants were selected from mutant mixtures based on cell density using differential sedimentation rates. Of the mutant strains obtained in the top phase of the separation medium, 72% showed a higher lipid content than the wild-type strain. One mutant strain exhibited a 57.3% enhanced lipid content and a 9.3% lower heating value (LHV), both indicators of direct combustion fuel performance, compared to the wild-type strain. Our findings indicate that sedimentation rate-based strain selection allows for the easy and rapid screening of high-lipid content algal strains for the use of microalgae as direct combustion fuels.

The spatial distribution of total mercury in sediments in the Yatsushiro Sea, Japan

The Yatsushiro Sea in Japan is contaminated with mercury in wastewater discharge from the Chisso Company, which produced acetaldehyde from 1932 onwards. In this study, we investigated the current spatial distribution of total mercury (T-Hg) in sediments, both at the surface and at different depths, using 43 sediment cores and 22 surface sediment samples collected from the Yatsushiro Sea in August 2017. Altogether, 821 surface and core samples were analyzed for their T-Hg concentrations. Most of the mercury that was discharged from Chisso remained either in, or around the exit of, Minamata Bay, but some had been transported from Minamata Bay to the Nagashima Sea. We estimated that almost 51 and 6 tons of mercury had accumulated in the Yatsushiro and the Amakusa Sea areas, respectively. The amount of acetaldehyde produced in Chisso over time was correlated with the T-Hg concentrations in the sediments from the Yatsushiro Sea.

Assessment of a coastal lagoon metal distribution through natural and anthropogenic processes (SE, Brazil)

The present study intends to assess the metal pollution of a eutrophic coastal lagoon, analyzing the long-term and actual metal content in surface sediments, suspended particles, aquatic macrophyte and fish species, and the loads emitted from natural processes and anthropogenic sources, including the relative emission of domestic untreated sewage. Distribution indicated contamination of suspended particles with Cd and the predominance of Pb in the bioavailable form in surface sediments which may explain Cd and Pb contamination in fish. Domestic untreated sewage was an important source of Cu and due to the lagoon's management, this source may be increasing the metal content in the lagoon's surface sediments. Soil loss, atmospheric deposition and solid waste disposal also contributed to metal inputs to the lagoon. Extensive contamination has been prevented by the lagoon's management such as sandbar opening. Metal retention within the watershed soils reduce the effective metal transference and lagoon pollution.

Historical records of mercury deposition in dated sediment cores reveal the impacts of the legacy and present-day human activities in Todos os Santos Bay, Northeast Brazil

We determined depth profiles of total mercury (T-Hg) in six ²¹⁰Pb-dated sediment cores from Todos os Santos Bay to reconstruct the history of anthropogenic Hg accumulation. We also assessed superficial sediments samples from five estuaries. T-Hg concentrations (5-3500 μg kg^-1) presented a large spatial and temporal variability. T-Hg concentrations in Ribeira Bay increased up to 200-fold along time, whereas the fluxes of T-Hg are substantially higher (up to 10,000 fold) than present-day wet deposition for industrialized areas. Sedimentary records indicate that a chlor-alkali plant has been the main source of Hg pollution until the present, although the T-Hg records suggest that harbor, shrimp farming, and oil refinery activities, besides Hg atmospheric depositions, are important across the bay. Sediments in the Ribeira Bay act as an important Hg sink. If sediments are eroded or disturbed, they may release Hg, thus posing a serious risk to wildlife and ecosystem health. CAPSULE: Sedimentary cores provide data on preindustrial levels and also anthropogenic fluxes of Hg for the appraisal of the magnitude, processes and potential risks of the contamination.

Polybrominated diphenyl ethers (PBDEs) in core sediments from creek ecosystem: occurrence, geochronology, and source contribution

The levels of 15 polybrominated diphenyl ether (PBDE) congeners in grab sediment and sediment cores from the Thane creek were monitored for their spatial and temporal distribution. Total PBDE (ΣPBDE) concentrations in grab sediments were ranging from 15.98 to 132.72 ng g^-1 dry weight. BDE-209 was the most abundant congener with percentage contribution in the range of 19-35% to total PBDEs. Total PBDE show multimode concentration with depth in sediment, among which mode at a depth of 10 cm is predominant. Results of sediment core also indicates PBDEs were enormously used in last two decades in surrounding area. Sedimentation rate at the creek was also evaluated using Pb²¹⁰ dating technique. Average percentage contribution of commercial penta-BDE (f_P), octa-BDE (f_O), and deca-BDE (f_D) to the profile found in sediments collected across Thane creek were 24 ± 5, 5 ± 1 and 69 ± 7% (p < 0.001) respectively. Levels of all measured PBDEs in sediment met with guideline values except for the penta-BDE (total, BDE-99 and BDE-100) at few locations.

Historical trends and assessment of radionuclides and heavy metals in sediments near an abandoned mine, Lavrio, Greece

Two sediment cores (coastal and offshore) and surface sediments were collected near an abandoned mine area in the marine environment of Oxygono Bay at Lavreotiki peninsula to investigate temporal and spatial variations among radionuclides and trace metals/major elements. Lavreotiki was and still is well known for the mining and metallurgical activities, which lasted from ancient times to nowadays (early 1980s). Gamma-ray and X-ray fluorescence measurements were held to determine the radionuclide and trace metal/major element concentrations, respectively. The sedimentation rate at Oxygono Bay coastal core was determined using the ²¹⁰Pb and ¹³⁷Cs tracers, while the enrichment factors were estimated to assess the anthropogenic influence due to metals in a spatial (surface sediments) and a temporal (coastal core sediments) basis. The mass flux at the coastal core was utilized to provide a baseline information at Lavreotiki peninsula. The trace metal/major element profiles were indeed associated with the mining activity in the area, revealing the mining history. The ERICA Tool was incorporated to estimate the dose rates due to natural and ¹³⁷Cs radioactivity in the marine organisms and the values were found below the screening levels.

Engineering rheology of electrolytes using agar for improving the performance of bioelectrochemical systems

The present study is focused on enhancing the rheological properties of the electrolyte and eliminating sedimentation of microorganisms/flocs without affecting the electron transfer kinetics for improved bioelectricity generation. Agar derived from polysaccharide agarose (0.05-0.2%, w/v) was chosen as a rheology modifying agent. Electroanalytical investigations showed that electrolytes modified with 0.15% agar display a nine-fold increase in current density (1.2 mA/cm²) by a thermophilic strain (Geobacillus sp. 44C, 60 °C) when compared with the control. Sodium phosphate buffer (0.1 M, pH 7) electrolyte with riboflavin (0.1 mM) was used as the control. Electrolytes modified with 0.15% agar significantly improved chemical oxygen demand removal rates. This developed electrolyte will aid in improving bioelectricity generation in Bioelectrochemical Systems (BES). The developed strategy avoids the use of peristaltic pumps and magnetic stirrers, thereby improving the energy efficiency of the process.

Geochronology and sources of heavy metal pollution in sediments of Istanbul Strait (Bosporus) outlet area, SW Black Sea, Turkey

Geochemical and sedimentological analyses and radionuclide (²¹⁰Pb and ¹³⁷Cs) dating of three cores from the Bosporus outlet area of the Black Sea, north of Istanbul, were conducted to assess the sources and history of heavy metal pollution. The sedimentary succession in the shelf core KD12-01 consists mainly of clay (49-80%) and silt (15-41%). Radionuclide dating of the core indicates that it consists of old sediments that are uncontaminated with heavy metals. In contrast, cores KD12-04 and KD12-07 recovered from -350 m and -304 mm in the upper slope area represent sediments consisting of silt and clay that were deposited since at least the last 120 years and 60 years, respectively. The latter core contains two mass-flow units represented by relatively old sedimentary material according to the low ²¹⁰Pb activity and relatively low heavy metal contents. The upper 40 and 48 cm of cores KD 12-04 and KD 12-07 represent sediments deposited since 1970s and 1980s that are significantly polluted with Cu, Ni, Zn, Mo, Pb and Cr, Cu, Co, Ni, Mo, Pb, Zn, respectively. However, high Pb and Cr concentrations with high TOC contents date back to early part of the 20th century in core KD 12-04. The geochemical data, together with the high ¹³⁷Cs concentrations of the contaminated sediments, strongly suggest that the pollution is mainly delivered to the western and north western Black Sea by the large European rivers, from there transported to the study area by the rim current, and deposited in the sediments under anoxic conditions.

Metabolic and oxidative stress responses of the jellyfish Cassiopea to pollution in the Gulf of Aqaba, Jordan

Physiological responses of jellyfish to pollution are virtually overlooked. We measured the activity of two glycolytic enzymes (pyruvate kinase (PK) and lactate dehydrogenase (LDH)), lipid peroxidation (LPO), protein and chlorophyll a content in the jellyfish Cassiopea sp. from polluted and reference sites along the Gulf of Aqaba, Jordan. In jellyfish from polluted sites, low PK/LDH ratios and high LDH activity clarify their reliance on anaerobic metabolism. PK and LDH were positively correlated in the jellyfish. While medusae from polluted sites showed no signs of oxidative stress damage, protein content was significantly lower. This might suggest protein utilization for energy production needed for maintenance. Unchanged LPO in polluted sites indicates the ability of jellyfish to keep reactive oxygen species under control. Overall these results suggest that the jellyfish seems to tolerate the current levels of pollution at the studied sites and they might be anaerobically poised to live at such habitats.

A 210Pb chronological study in sediments from poços de caldas alkaline massif (PCAM), Brazil

The Constant Flux and Constant Sedimentation (CF:CS) of supported/excess ²¹⁰Pb model was successfully used to study sediment profiles from Antas stream, located in the region of Poços de Caldas city, Minas Gerais State, Brazil. Historical changes in the region were tracked from evaluating the sedimentation rate by the ²¹⁰Pb method. In that site, Osamu Utsumi mine was the first mining-industrial complex for the production of concentrated uranium in Brazil. Four sediment testimonies were sampled along Antas stream in order to determine sedimentation rates using ²¹⁰Pb as geochronometer. ²¹⁰Pb and ²³⁸U activity concentrations were determined in sediment samples by alpha spectrometry, allowing to find the excess ²¹⁰Pb present in the sediments. Additionally, the main oxides, organic matter, particles size and water composition were determined in order to assist the results interpretation from radionuclides data. The results allowed find one (profile PKS-4) or two (profiles PKS-1, PKS-2 and PKS-3) sedimentation rates, probably due to changes in the sediments input regime in the region. The sedimentation rates were in the range between 0.26 and 0.94 g/cm².year, corresponding to the interval of linear sedimentation rate of 0.21 - 0.92 cm/year. The deposition year in the bottom of PKS-4 profile as estimated from the sedimentation rate coincided with the construction year of Bortolan dam (1956). Large touristic interventions carried out at Poços de Caldas city from 1920s coupled to unbridled urbanization, industrialization and demographic growth there in the second half of the twentieth century possibly caused the changes found in the sedimentation rates.

Geochemical behavior, environmental availability, and reconstruction of historical trends of Cu, Pb, and Zn in sediment cores of the Cananéia-Iguape coastal system, Southeastern Brazil

The Cananéia-Iguape system is located in a coastal region of southeastern Brazil, recognized by UNESCO as an Atlantic Forest Biosphere Reserve. This system has suffered substantial environmental impacts due to the opening of an artificial channel and by past intensive mining activities. In this paper was performed the sequential chemical extraction of Cu, Pb, and Zn, on previously described sediment cores, and the statistical treatment of the data, allowing to estimate the remobilization geochemical behavior, the available content and the trend of accumulation between 1926 and 2008. The maximum available level (sum of all mobile fraction) were, in mgkg^-1, 18.74 for Cu, 177.55 for Pb and 123.03 for Zn. Considering its environmental availability, Pb remains a concern in the system. It was possible to recognize the anthropic contribution of Pb, being the mining activities considered the only potential source of this metal in the region.

Determination of sedimentation, diffusion, and mixing rates in coastal sediments of the eastern Red Sea via natural and anthropogenic fallout radionuclides

The Red Sea is a unique ecosystem with high biodiversity in one of the warmest regions of the world. In the last five decades, Red Sea coastal development has rapidly increased. Sediments from continental margins are delivered to depths by advection and diffusion-like processes which are difficult to quantify yet provide invaluable data to researchers. Beryllium-7, lead-210 and ceseium-137 were analyzed from sediment cores from the near-coast Red Sea near Jeddah, Saudi Arabia. The results of this work are the first estimates of diffusion, mixing, and sedimentation rates of the Red Sea coastal sediments. Maximum chemical diffusion and particle mixing rates range from 69.1 to 380cm^-2y^-1 and 2.54 to 6.80cm^-2y^-1, respectively. Sedimentation rate is constrained to approximately 0.6cm/yr via multiple methods. These data provide baselines for tracking changes in various environmental problems including erosion, marine benthic ecosystem silting, and particle-bound contaminant delivery to the seafloor.

The impact of submarine copper mine tailing disposal from the 1970s on Repparfjorden, northern Norway

We investigate the state of sedimentological environment and contaminant status of Repparfjorden (N Norway) impacted by submarine disposal of mine tailings during the 1970s using sedimentological and geochemical properties of seventeen sediment cores. The impact of tailings disposal is mainly restricted to the inner fjord where the discharge occurred. Sediment cores retrieved from the inner fjord contain layers of mine tailings up to 9-cm thick, 3-9cm below the seafloor. Spreading of the tailing-related metal Cu and particles is limited to the inner fjord and to a 2cm layer in one core from the outer fjord. Two interrelated factors, fjord morphology and sedimentation rate, controlled the distribution of contaminant-laden tailings in the fjord. The mobility of Cu from buried contaminated sediments to the sediment-water interface in the inner fjord indicates that benthic communities have been continuously exposed to elevated Cu concentrations for nearly four decades.

Anthropic influences on the sedimentation rates of lakes situated in different geographic areas

The aim of this study is to determine the effects of natural and anthropic events occurring in the last 30 years in the catchment areas of four Romanian lakes (St. Anna Lake, Red Lake, Vârşolţ Lake and Matiţa Lake) originating from four different geomorphologic areas. A total of eleven sediment cores have been processed for age and sedimentation rate determination using the ²¹⁰Pb dating method. Total ²¹⁰Pb was measured via alpha spectrometry by ²¹⁰Po using PIPS detectors, while supported ²¹⁰Pb was measured by ²²⁶Ra using HPGe detectors. Ages and sedimentation rates were calculated using the CRS model. The values of the sedimentation rates have grown multiply in the last three decades: 2.66 times in case of the St. Anna Lake (from 0.06 ± 0.01 g/cm²y to 0.16 ± 0.02 g/cm²y), up to 6.72 times in case of Red Lake (0.36 ± 0.04 g/cm²y to 2.42 ± 0.36 g/cm²y), 4.02 times in case of Vârşolţ Lake (04 g/cm²y to 1.53 ± 0.18 g/cm²y) and up to 16.18 times in case of Matiţa Lake (0.27 ± 0.03 g/cm²y to 4.37 ± 0.32).

Regional environmental change and human activity over the past hundred years recorded in the sedimentary record of Lake Qinghai, China

Environmental change and human activity can be recorded in sediment cores in aquatic systems such as lakes. Information from such records may be useful for environmental governance in the future. Six sediment cores were collected from Lake Qinghai, China and its sublakes during 2012 and 2013. Measurements of sediment grain-size fractions indicate that sedimentation in the north and southwest of Lake Qinghai is dominated by river input, whereas that in Lake Gahai and Lake Erhai is dominated by dunes. The sedimentation rates in Lake Qinghai were calculated to be 0.101-0.159 cm/y, similar to the rates in other lakes on the Qinghai-Tibetan Plateau. Using these data and sedimentation rates from the literature, we compiled the spatial distribution of sedimentation rates. Higher values were obtained in the three main areas of Lake Qinghai: two in river estuaries and one close to sand dunes. Lower values were measured in the center and south of the lake. Measurements of total organic carbon (TOC), total nitrogen (TN), phosphorus concentrations, and TOC/TN ratios in three cores (QH01, QH02, and Z04) revealed four horizons corresponding to times of increased human activity. These anthropogenic events were (1) the development of large areas of cropland in the Lake Qinghai watershed in 1960, (2) the beginning of nationwide fertilizer use and increases in cropland area in the lake watershed after 1970, (3) the implementation of the national program "Grain to Green," and (4) the rapid increase in the tourism industry from 2000. Profiles of Rb, Sr concentrations, the Rb/Sr ratio, and grain-size fraction in core Z04 indicate that the climate has become drier over the past 100 years. Therefore, we suggest that lake sediments such as those in Lake Qinghai are useful media for high-resolution studies of regional environmental change and human activity.

Heavy metals and nutrients (carbon, nitrogen, and phosphorus) in sediments: relationships to land uses, environmental risks, and management

Management of sediments in polluted rivers requires an inventory of sediment quantities as well as their nutrient and metal contents and the chemical forms of pollutants. We investigated the influence of three major land uses (i.e., orange plantation-OP, OP + residential + industrial-OPRI, and residential + industrial-RI) on the quality of surface sediments (0-20 cm below water/sediment interface) at the Sanyang Wetland (China). The total contents of metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) and nutrients (C, N, and P) as well as metal speciation in sediments were examined. GIS technology was used to estimate the volume of sediments needed to calculate the amounts of stored nutrients and metals in sediments. The surface sediments in the 3.2-km² study area contain more than 2800 Mg C, 200 Mg N, and 100 Mg P. OPRI and RI land uses contribute more total C, N, P, Zn, and Cd to sediments than OP land use. High contents of C, N, and P may provide options to recycle the sediments as fertilizer but must be used with caution due to high levels of metals. Total Cd in sediments is at an order of magnitude (up to 59 mg kg-1) higher than the Level III criterion in the Chinese Environmental Quality Standards for Soil. Sediments in all land uses have very high risks due to >50% exchangeable + carbonate-bound Zn, Ni, and Cd. It is suggested that toxicity tests be conducted to better assess the environmental risks associated with any potential use of sediments.

Offshore sediments record the history of onshore iron ore mining in Goa State, India

Environmental magnetic and geochemical analyses combined with ²¹⁰Pb dating were carried out on a sediment core off Goa from Arabian Sea to reconstruct the sedimentation history of last three and a half centuries and to investigate the impact of onshore iron ore mining on the offshore sedimentation. A drastic increase in sedimentation rate and mineral magnetic concentration parameters divides the core into two units (1 & 2) at a depth of 41cm (1982CE). The high magnetic susceptibility values in Unit 1 sediments are coeval with increased iron ore production on land and illustrate the role of terrestrial mining on the increased offshore sedimentation. The early diagenetic signals were observed in Unit 2 of the core with low concentration parameters, coarse magnetic grain size and magnetically hard mineralogy. The geochemical data of the core also record the Little Ice Age (LIA) climatic events of Dalton and Maunder solar minima.

Variation of sedimentation rate in the semi-enclosed bay determined by 137Cs distribution in sediment (Kaštela Bay, Croatia)

Purpose of this research was to study the rate at which the semi-enclosed bay such as the Kaštela Bay reacts to the coastal processes of industrialization and urbanization, the extent of the influence of human activities on the bay, and the sediment distribution affected by anthropogenic influence. Temporal and spatial sedimentation rate variations were observed between three studied periods: 1954-2005, 1963-2005/2006, and 1986-2005/2006. Sedimentation rates were in the following ranges: 0.29-0.49 cm/yr for the 1954-2005 period, 0.58-0.95 cm/yr for the 1963-2005/2006 period, and 0.50-1.32 cm/yr for the 1986-2005/2006 period. The average total sedimentation rates for three periods were 0.41 cm/yr, 0.81 cm/yr, and 0.61 cm/yr, respectively. Sedimentation rate for the individual 1963-1986 period marked with two ¹³⁷Cs marker peaks was in the 0.65-1.30 cm/yr range, while the mean value was 1.06 cm/yr. Long-term sedimentation rate increase in the whole Kaštela Bay was observed and clearly connected to the industrialization and urbanization processes in the coastal area. These processes reflect very quickly, in terms of years, in the sedimentation rates. Intensive anthropogenic activities in the coastal area are reflected in the whole bay depending on the amount of the discharged sediment material, topography of the sea bottom, and water currents. Some localized areas of sediment accumulation may form.

Heavy metal accumulation during the last 30 years in the Karnaphuli River estuary, Chittagong, Bangladesh

Heavy metal contamination of aquatic environment has attracted global attention owing to its abundance, persistence, and environmental toxicity, especially in developing countries like Bangladesh. Five heavy metals, namely chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) were investigated in surface and core sediments of the Karnaphuli River (KR) estuary in Chittagong, Bangladesh, in order to reveal the heavy metal contamination history in estuarine sediments and its response to catastrophic events and human activities. The surface sediment was predominantly composed of silt and sand, and the surface sediment was contaminated with Cr and Pb. Based on the ²¹⁰Pb chronology, the sedimentation rate in the inter-tidal zone of KR estuary was 1.02 cm/a before 2007, and 1.14 cm/a after 2008. The core sediment collected from 8 to 20 cm below the surface mainly originated from terrestrial materials induced by catastrophic events such as cyclone, heavy rainfall and landslides in 2007 and 2008. The values of contamination factor (CF) showed that the sediment became moderately contaminated with Cr and Pb in the last 30 years. The variation and accumulation of heavy metals in core sediment before 2000 was mainly related to natural variations in sediment sources; however, in subsequent years, the anthropogenic inputs of heavy metals have increased due to rapid physical growth of urban and industrial areas in the Chittagong city. In general, the accumulation pattern of heavy metals after normalization to Aluminum in sediments of KR estuary indicated an accelerated rate of urbanization and industrialization in the last 30 years, and also suggested the influence of natural catastrophic event on estuarine environment.

Temporal variation of sedimentation rates and potential factors influencing those rates over the last 100years in Bohai Bay, China

Fourteen sediment cores were collected from Bohai Bay, China, which is close to the fast-developing megacities such as Beijing and Tianjin, and dated using excess Pb-210 and Cs-137. Using the constant rate of supply model (CRS), the temporal variation of sedimentation rates over the last 100years in Bohai Bay was determined, and its main factors influencing sedimentation rates were discussed. The sedimentation rates before 1980 were relatively stable, ranging from 0.26±0.04g/(cm²·y) in 1920 to 0.39±0.08g/(cm²·y) in 1980. A gradual increase in sedimentation rate was found from 0.39±0.08g/(cm²·y) in 1980 to 0.84±0.13g/(cm²·y) in 2010. Riverine input was the main factors influencing sedimentation rates in Bohai Bay before 1980. After 1980, the accelerated increase in sedimentation rate may be attributed to the large-scale reclamation along the coastline. It is worth noting that eutrophication caused by an increase in sewage discharge and overuse of chemical fertilizer, also may influence recent acceleration in sedimentation rate.

Effects of pollution on the geochemical properties of marine sediments across the fringing reef of Aqaba, Red Sea

The Gulf of Aqaba is of significant strategic and economic value to all gulf-bordering states, particularly to Jordan, where it provides Jordan with its only marine outlet. The Gulf is subject to a variety of impacts posing imminent ecological risk to its unique marine ecosystem. We attempted to investigate the status of metal pollution in the coastal sediments of the Jordanian Gulf of Aqaba. The distribution of Cd, Cr, Zn, Cu, Pb, Al, Fe, and Mn concentrations were determined in trapped and bottom-surface sediments at three selected sites at different depths. In addition, monthly sedimentation rates at varying water depths were also estimated at each sampling site using sediment traps. The high concentrations of Cd, Cr, Zn were recorded at the Phosphate Loading Birth (PLB) site followed by the Industrial Complex (IC) site indicating their dominant anthropogenic source (i.e., the contribution of industrial activities). However, Fe, Al, and Mn contents were related to inputs from the terrigenous (crustal) origin. Except for Al, Fe and Mn at the PLB site, the concentrations of metals exhibited a decreasing trend with increasing water depth (distance from the shoreline). The PLB site also showed the highest sedimentation rate which decreased with increasing water depth. The Enrichment factors (EFs) showed that Cd was the most enriched element in the sediment (indicating that Cd pollution is widespread), whereas the least enriched metal in sediments was Cu. EF values suggested that the coastal area is impacted by a combination of human and natural sources of metals, where the anthropogenic sources are intense in the PLB site (north of Gulf of Aqaba). The MSS area is potentially the least polluted, consistent with being a marine reserve. The IC sediments have been found to be impacted by human activities but less intensely compared to the PLB area. These results suggested that there are two sources of metals in sediments; the primary source is likely closer to PLB, while the secondary is nearby the IC.

Predicting dredging-associated effects to coral reefs in Apra Harbor, Guam - Part 2: Potential coral effects

Coral reefs are in decline worldwide due to anthropogenic stressors including reductions in water and substratum quality. Dredging results in the mobilization of sediments, which can stress and kill corals via increasing turbidity, tissue damage and burial. The Particle Tracking Model (PTM) was applied to predict the potential impacts of dredging-associated sediment exposure on the coral reef ecosystems of Apra Harbor, Guam. The data were interpreted using maps of bathymetry and coral abundance and distribution in conjunction with impact parameters of suspended sediment concentration (turbidity) and sedimentation using defined coral response thresholds. The results are presented using a "stoplight" model of negligible or limited impacts to coral reefs (green), moderate stress from which some corals would be expected to recover while others would not (yellow) and severe stress resulting in mortality (red). The red conditions for sediment deposition rate and suspended sediment concentration (SSC) were defined as values exceeding 25 mg cm(-2) d(-1) over any 30 day window and >20 mg/l for any 18 days in any 90 day period over a column of water greater than 2 m, respectively. The yellow conditions were defined as values >10 mg cm(-2) d(-1) and <25 mg cm(-2) d(-1) over any 30 day period, and as 20% of 3 months' concentration exceeding 10 mg/l for the deposition and SSC, respectively. The model also incorporates the potential for cumulative effects on the assumption that even sub-lethal stress levels can ultimately lead to mortality in a multi-stressor system. This modeling approach can be applied by resource managers and regulatory agencies to support management decisions related to planning, site selection, damage reduction, and compensatory mitigation.

Predicting dredging-associated effects to coral reefs in Apra Harbor, Guam - Part 1: Sediment exposure modeling

Model studies were conducted to investigate the potential coral reef sediment exposure from dredging associated with proposed development of a deepwater wharf in Apra Harbor, Guam. The Particle Tracking Model (PTM) was applied to quantify the exposure of coral reefs to material suspended by the dredging operations at two alternative sites. Key PTM features include the flexible capability of continuous multiple releases of sediment parcels, control of parcel/substrate interaction, and the ability to efficiently track vast numbers of parcels. This flexibility has facilitated simulating the combined effects of sediment released from clamshell dredging and chiseling within Apra Harbor. Because the rate of material released into the water column by some of the processes is not well understood or known a priori, the modeling approach was to bracket parameters within reasonable ranges to produce a suite of potential results from multiple model runs. Sensitivity analysis to model parameters is used to select the appropriate parameter values for bracketing. Data analysis results include mapping the time series and the maximum values of sedimentation, suspended sediment concentration, and deposition rate. Data were used to quantify various exposure processes that affect coral species in Apra Harbor. The goal of this research is to develop a robust methodology for quantifying and bracketing exposure mechanisms to coral (or other receptors) from dredging operations. These exposure values were utilized in an ecological assessment to predict effects (coral reef impacts) from various dredging scenarios.

Influence of Sedimentation Rate on the Metal Contamination in Sediments of Bohai Bay, China

Metal concentration in marine sediments is influenced by sedimentation rate. In this study, the metal concentration in sediments of Bohai Bay, China, was adjusted by sedimentation rate, which was derived from the radionuclide dating method. The results showed that the sedimentation rate of Bohai Bay sediments increased from 0.3 to 0.55 g/a over time, especially in the last 30 years since the economic reform in China. The sequence of metal concentrations (mg/kg) is: Cr(97.41) > Zn(73.14) > Cu(20.59) > Pb(16.42) > Cd(0.49). Through the adjustment, the change of metal concentration in sediment cores increased obviously from bottom to surface sediments. It indicated that the increasing sedimentation rate of Bohai Bay in recent years diluted the metal concentration in the sediment.

Short-term impact of deep sand extraction and ecosystem-based landscaping on macrozoobenthos and sediment characteristics

We studied short-term changes in macrozoobenthos in a 20m deep borrow pit. A boxcorer was used to sample macrobenthic infauna and a bottom sledge was used to sample macrobenthic epifauna. Sediment characteristics were determined from the boxcore samples, bed shear stress and near-bed salinity were estimated with a hydrodynamic model. Two years after the cessation of sand extraction, macrozoobenthic biomass increased fivefold in the deepest areas. Species composition changed significantly and white furrow shell (Abra alba) became abundant. Several sediment characteristics also changed significantly in the deepest parts. Macrozoobenthic species composition and biomass significantly correlated with time after cessation of sand extraction, sediment and hydrographical characteristics. Ecosystem-based landscaped sand bars were found to be effective in influencing sediment characteristics and macrozoobenthic assemblage. Significant changes in epifauna occurred in deepest parts in 2012 which coincided with the highest sedimentation rate. We recommend continuing monitoring to investigate medium and long-term impacts.

Corals persisting in naturally turbid waters adjacent to a pristine catchment in Solomon Islands

Few water quality measurements exist from pristine environments, with fewer reported studies of coastal water quality from Solomon Islands. Water quality benchmarks for the Solomons have relied on data from other geographic regions, often from quite different higher latitude developed nations, with large land masses. We present the first data of inshore turbidity and sedimentation rate for a pristine catchment on Isabel Island. Surveys recorded relatively high coral cover. The lowest cover was recorded at 22.7% (Jejevo) despite this site having a mean turbidity (continuous monitoring) of 32 NTU. However, a similar site (Jihro) was significantly less turbid (2.1 mean NTU) over the same period. This difference in turbidity is likely due to natural features of the Jihro River promoting sedimentation before reaching coastal sites. We provide an important baseline for Solomon Island inshore systems, whilst demonstrating the importance of continuous monitoring to capture episodic high turbidity events.